linux-kernel - Re: [PATCH v7 01/10] lib/group_cpus: Add group_masks_cpus

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Message-ID: <2b70fbd3-d63d-4bd3-8500-e14c41fc64b9@oracle.com>
Date: Fri, 11 Jul 2025 09:28:12 +0100
From: John Garry <john.g.garry@...cle.com>
To: Daniel Wagner <wagi@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc: Aaron Tomlin <atomlin@...mlin.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Costa Shulyupin
 <costa.shul@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Waiman Long <llong@...hat.com>, Ming Lei <ming.lei@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mel Gorman <mgorman@...e.de>, Hannes Reinecke <hare@...e.de>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-nvme@...ts.infradead.org, megaraidlinux.pdl@...adcom.com,
        linux-scsi@...r.kernel.org, storagedev@...rochip.com,
        virtualization@...ts.linux.dev, GR-QLogic-Storage-Upstream@...vell.com
Subject: Re: [PATCH v7 01/10] lib/group_cpus: Add group_masks_cpus_evenly()

On 02/07/2025 17:33, Daniel Wagner wrote:

/s/group_masks_cpus_evenly/group_mask_cpus_evenly/

> group_mask_cpus_evenly() allows the caller to pass in a CPU mask that
> should be evenly distributed. This new function is a more generic
> version of the existing group_cpus_evenly(), which always distributes
> all present CPUs into groups.
> 
> Signed-off-by: Daniel Wagner <wagi@...nel.org>
> ---
>   include/linux/group_cpus.h |  3 +++
>   lib/group_cpus.c           | 64 +++++++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/group_cpus.h b/include/linux/group_cpus.h
> index 9d4e5ab6c314b31c09fda82c3f6ac18f77e9de36..d4604dce1316a08400e982039006331f34c18ee8 100644
> --- a/include/linux/group_cpus.h
> +++ b/include/linux/group_cpus.h
> @@ -10,5 +10,8 @@
>   #include <linux/cpu.h>
>   
>   struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks);
> +struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
> +				       const struct cpumask *cpu_mask,
> +				       unsigned int *nummasks);
>   
>   #endif
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index 6d08ac05f371bf880571507d935d9eb501616a84..00c9b7a10c8acd29239fe20d2a30fdae22ef74a5 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -8,6 +8,7 @@
>   #include <linux/cpu.h>
>   #include <linux/sort.h>
>   #include <linux/group_cpus.h>
> +#include <linux/sched/isolation.h>
>   
>   #ifdef CONFIG_SMP
>   
> @@ -425,6 +426,59 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
>   	*nummasks = min(nr_present + nr_others, numgrps);
>   	return masks;
>   }
> +EXPORT_SYMBOL_GPL(group_cpus_evenly);
> +
> +/**
> + * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> + * @numgrps: number of groups

this comment could be a bit more useful

> + * @cpu_mask: CPU to consider for the grouping

this is a CPU mask, and not a specific CPU index, right?

> + * @nummasks: number of initialized cpusmasks
> + *
> + * Return: cpumask array if successful, NULL otherwise. And each element
> + * includes CPUs assigned to this group.
> + *
> + * Try to put close CPUs from viewpoint of CPU and NUMA locality into
> + * same group. Allocate present CPUs on these groups evenly.
> + */
> +struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
> +				       const struct cpumask *cpu_mask,
> +				       unsigned int *nummasks)
> +{
> +	cpumask_var_t *node_to_cpumask;
> +	cpumask_var_t nmsk;
> +	int ret = -ENOMEM;
> +	struct cpumask *masks = NULL;
> +
> +	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
> +		return NULL;
> +
> +	node_to_cpumask = alloc_node_to_cpumask();
> +	if (!node_to_cpumask)
> +		goto fail_nmsk;
> +
> +	masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
> +	if (!masks)
> +		goto fail_node_to_cpumask;
> +
> +	build_node_to_cpumask(node_to_cpumask);
> +
> +	ret = __group_cpus_evenly(0, numgrps, node_to_cpumask, cpu_mask, nmsk,
> +				  masks);

maybe it's personal taste, but I don't think that it's a good style to 
always pass through 'fail' labels, even if we have not failed in some step

> +
> +fail_node_to_cpumask:
> +	free_node_to_cpumask(node_to_cpumask);
> +
> +fail_nmsk:
> +	free_cpumask_var(nmsk);
> +	if (ret < 0) {
> +		kfree(masks);
> +		return NULL;
> +	}
> +	*nummasks = ret;
> +	return masks;
> +}
> +EXPORT_SYMBOL_GPL(group_mask_cpus_evenly);
> +
>   #else /* CONFIG_SMP */
>   struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
>   {
> @@ -442,5 +496,13 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
>   	*nummasks = 1;
>   	return masks;
>   }
> -#endif /* CONFIG_SMP */
>   EXPORT_SYMBOL_GPL(group_cpus_evenly);
> +
> +struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
> +				       const struct cpumask *cpu_mask,
> +				       unsigned int *nummasks)
> +{
> +	return group_cpus_evenly(numgrps, nummasks);
> +}
> +EXPORT_SYMBOL_GPL(group_mask_cpus_evenly);
> +#endif /* CONFIG_SMP */
>